1. Field of the Invention
The present invention relates to a charger system, a charging method and a secondary battery system, and more particularly, suitably applied to a charger system, a charging method and a secondary battery system in which a secondary battery is charged using electric power given from an AC power source.
2. Description of the Related Art
The demand of portable compact electronic appliances which are exemplified by small-sized headphone stereos, VTRs incorporated with cameras, and mobile communication terminals has been increasing. These compact electronic appliances use secondary batteries having large capacities as power sources, and the secondary batteries can be charged by being supplied with charging currents from associated charger systems when power of the secondary batteries is lowered.
In FIG. 1, numeral 1 shows a charger system, in which a secondary battery 5 is charged using electric power obtained from an AC power source 2. In other words, the charger system 1 inputs AC power given from the AC power source 2 into a transformer 3. The transformer 3 which is composed of a primary coil L1 and a secondary coil L2 sends out a desired voltage after dividing the voltage of the given AC power in accordance with a ratio between the respective numbers of windings of the primary coil L1 and the secondary coil L2. Further, the charger system 1 converts the AC power of the desired voltage into DC power by rectification with a diode D1 and smoothing with a capacitor C1. Furthermore, the charger system 1 prepares a predetermined charging standard voltage or a predetermined charging standard current by performing a constant current/constant voltage processing on the thus obtained DC power with a charging control section 4. The charger system 1 charges the secondary battery 5 with stable DC power thus obtained.
By the way, in the charger system 1 configured as described above, a DC voltage is extracted by rectifying an AC voltage with the diode D1 and moreover, pulsating components are eliminated from the DC voltage with the capacitor C1, and then the secondary battery 5 is charged by supplying the obtained DC voltage. However, in the case where a secondary battery having a large capacity is used as a power source, a high current must be supplied as a charging current for charging the secondary battery and the capacitor C1 must have a large capacitance for smoothing such a high charging current.
However, external dimensions of capacitors generally tend to be large in proportion to their capacitance values. Accordingly, in the charger system which has the capacitor C1 having such a large capacitance value, its miniaturization is a difficult in that a volume for placing the capacitor C1 has to be reserved. In addition, such a high charging current has another problem in that heat is generated by the capacitor C1.